Nuclear radiation detecting means and transmission system connecting same to remote indicator means



Aprxl 26, 1966 R. STONE ETAL 3,

NUCLEAR RADIATION DETECTING MEANS AND TRANSMISSION SYSTEM CONNECTING SAME TO REMOTE INDICATOR MEANS Original Filed July 27, 1960 Tic. E.

INVENTORS 47 IMAM/FD R, .SMA/E MCf/OMS a. Mam owe BY JA'MES E coo/z United States Patent 13 Claims. (Cl. fi-83.6)

The present invention relates to nuclear radiation indicating systems and, particularly, to such systems for providing indications at a point remote from the point of radiation detection. While the present invention has utility in numerous and diverse applications, it has particular utility in connection with the operation of metallurgical furnaces and will be described in that connection.

This application is a continuation of our now abancloned application for United States Letters Patent, Serial Number 45,707, filed July 27, 1960.

The process of extracting iron from its ore involves the charging of a mixture of ore, coke and flux in proper proportions through a specially constructed charging chamber at the top of an extraction furnace of which a blast furnace is typical. It is important to know at all times the level of the charge within the furnace and whether the stock is evenly distributed therein. The level of the stock preferably should be maintained at a substantially constant height corresponding to the full capacity of the furnace, and should be evenly distributed in order to promote an even passage of the air blast therethrough.

The height of the stock in a furnace and the evenness of its distribution may readily be determined by the gauging system disclosed in United States Patent 3,133,191, issued May 12, 1964, to L. E. Stone, T. I. Radcliffe and G. W. Sower, entitled, Blast Furnace Stock Level Control. This gauging system utilizes nuclear radiation sources positioned at spaced elevations along two sides of the exterior of the furnace wall and projecting narrow beams of radiation, for example, gamma rays, through sealed ports of the furnace walls to Geiger tubes supported in correspondingly spaced positions on the opposite exterior wall surfaces of the furnace. The Geiger radiation detection tubes are energized by rectified alternating current supplied to the Geiger tube locations, and

the high impedance output circuits of these tubes are coupled through an amplifier to a rectifier system to derive bias potentials proportional in magnitude to the intensity of the incident radiation. Each such amplifier and its associated rectifier system are placed at the Geiger tube location by reason of the high impedance output circuit of the Geiger tube, and this is true also of a vacuum tube Schmitt trigger arrangement which is controlled by the developed bias potential to control the operation of a relay. A relatively low potential rectifier system is likewise included at the Geiger tube location to furnish excitation potentials for the amplifier stage, the Schmitt trigger arrangement, and the relay contacts which by way of a transmission circuit extending to a remote point control indicators and appropriate control relays for use in monitoring and controlling the level and distribution of the stock in the blast furnace. The use of the numerous electronic components in the equipments in proximity to "Ice the Geiger tube near the top of the blast furnace create maintenance and servicing problems due to their relatively inaccessible location. To minimize these difiiculties, it would be highly desirable to simplify the complexity of the top-of-furnace equipment, minimize the number of components which may be subject to ageing and failure during operation, and increase the overall reliability of the radiation detection equipment to the utmost practicable extent.

It is an object of the present invention to provide a novel nuclear radiation indicatingvsystem of simplified construction and substantially improved reliability.

It is a further object of the invention to provide a nuclear radiation indicating system which entirely avoids the use of any form of vacuum tube other than a Geiger radiation detection tube, and which by reason of this and the use both of high reliability semiconductor devices and a minimized number of electrical components (themselves possessing stable electrical characteristics) enables exceptionally high reliability of radiation indications over prolonged operational periods without need for close supervision, frequent recalibration, or maintenance.

It is an additional object of the invention to provide an improved nuclear radiation indicating system of sturdy construction and relatively low initial operating and maintenance costs, and one which exhibits unusual stability of its operational characteristics and readily permits the detection of radiation intensity at a relatively inaccessible point and its direct transmission through low impedance transmission circuits and in simple and reliable manner to a distant point for observation, use, direct calibration,

and monitoring.

Gther objects and advantages of the invention will appear as the detailed description thereof proceeds in the light of the drawings forming a part of this application and in which:

FIG. 1 is a circuit diagram showing the arrangement of a nuclear radiation indicating system embodying the present invention in a particular form; and

FIG. 2 illustrates a Geiger tube detector construction suitable for use in a modified form of the invention.

Referring now more particularly to FIG. 1, the indicating system includes a Geiger radiation detection tube 10 which may be of the Hallogen quenched type (such as an Anton type 313) which is energized at a unidirectional .voltage well above the plateau value of voltage in order to obtain increased detection sensitivity. This high unidirectional voltage is provided by a transformer 11 having a primary winding 12 energized from an alternating current source 13 through a conventional constant voltage transformer 14. The high voltage secondary winding 15 of the transformer 11 is connected through a current limiting protective resistor 16 and a semiconductor rectifier 17, which may be of the silicon diode rectifier type, to a condenser 18 and shunt connected resistor 19 across which the high unidirectional excitation voltage is developed. This unidirectional voltage is supplied through a resistor 20 to the anode of the Geiger tube It which in cludes the primary winding 21 of a transformer 22 in its cathode circuit. The value of the resistor 20 is selected to limit the current flow to the Geiger tube 10 and prevent sustained conductivity of the latter, thus providing external quenching safety for the Hallogen gas Geiger tube.

The transformer 22 includes a low impedance secondary winding 23 which is coupled through a low impedance shielded coaxial transmission line 24 to the primary winding 25 of a transformer 26 located at a remote point from the Geiger tube location. The transformer 26 includes a secondary winding 27 which is connected to a conductance control gate electrode 28 of a semiconductor conductance control device 29 having a cathode electrode 30 and an anode electrode 31. The semiconductor device 29 may be of any various well known trigger types, such as PNPN type 3A201-S silicon controlled switch manufactured by Solid State Products, Inc.

The characteristic of the device 29 is such that it remains nonconductive until a potential of positive polarity and of suitable magnitude is applied to its conductance control gate electrode 28 after which the device 29 becomes fully conductive with accompanying loss of conductivity control by the control gate electrode 28. A resistor 32 provides a conductive path between the control gate electrode 28 and cathode electrode 30 of the device 29, and series connected semiconductor diode rectifiers 33 and 34 are connected across the secondary winding 27 of thetransformer 26 to protect the device 29 from excessive positive over-voltage which might under certain circumstances be developed in the secondary winding 27 of the transformer 26. The semiconductor diode rectifiers 33 and 34 may conveniently be type IN605 manufactured by General Electric Company, and two such rectifiers are used in series to avoid excessive loading of the input circuit of the device 29. A third semiconductor rectifier device 35 is connected across the secondary winding 27 of the transformer 26 with a polarity opposite to the rectifier devices 33 and 34 and provides negative over-voltage protection for the device 29.

The anode electrode 31 of the device 29 is energized from the constant voltage transformer 14 through a semiconductor rectifier device 36, which may be of the above-mentioned type IN605, and is used to reduce the peak-inverse voltage applied between the anode electrode 31 and the cathode 30 of the device 29. This energizing circuit includes the operating winding 37 of a relay 38, in series with an adjustable resistor 39, a condenser 40 being connected in shunt to the relay winding 37. There is also connected in shunt to the latter an adjustable resistor 41 and meter current indicator 42 useful for monitoring and maintenance purposes. A condenser 43 is connected across the anode electrode 31 and cathode electrode 30 of the device 29.

Considering now the operation of the radiation indicating system just described, incident radiation on the Geiger tube produces, through the primary winding 21 of the transformer 22, current pulses having a repetition rate and intensity varying with the intensity of the incident radiation.

The operation of the Geiger tube 10 in this respect is entirely conventional and well known, the Geiger tube having high sensitivity by reason of its unconventional unidirectional potential energization above its plateau region. The transformer 22 is of the pulse translating type so that pulses are translated with high fidelity of the leading and lagging edges of the pulse wave form, and the secondary winding 23 has an impedance which properly matches the input impedance to the transmission line 24. The transformer 26 also is of the pulse transformer type and its input impedance is selected to match the output impedance of the transmission line 24. Thus the pulses generated by the Geiger tube 10, having normal pulse durations of approximately 200 microseconds and 10-volt amplitude, are translated by the transformers 22 and 26 and the transmission line 24 with such pulse differentiation as to reduce the pulse durations to approximately 1 to 2 microseconds with 1 to 2 volt amplitude at the secondary winding 27 of the transformer 26. It may be noted that the pulse transformer 22 matches the high impedance cathode circuit of the Geiger tube 10 to the low impedance of the transmission channel 24, and that the pulse transformer 26 likewise matches the low impedance of the transmission channel to the higher impedance of the input circuit of the control gate electrode 28 of the device 29. This enables the pulses generated in the cathode circuit of the Geiger tube 10 to be differentiated and transmitted with high translation efficiency over appreciable distances, which may be of the order of 1,000 feet or more without .the use of intervening pulse amplifiers and pulse shapers, to the site of the detection and utilization equipment which includes the semiconductor device 29. It may also be noted that the differentiation of the Geiger tube generated pulses-has the important advantage that it permits parallel operation of an appreciable number of Geiger tubes at the same location (and having a common cathode circuit) without causing impairment of radiation detection by reason of pulse pile-up.

The pulses appearing in the secondary winding 27 of the transformer 26 are applied to the control gate electrode 28 of the device 29 which is energized by the positive half cycles of potential applied to its anode electrode 31 through the diode rectifier 36 from the constant voltage transformer 14. The first pulse applied to the control gate electrode 28 during each positive half cycle of the voltage applied to the anode electrode 31 renders the device 29 fully conductive for the remainder of the positive half cycle of energizing voltage. This conductance control characteristic of the device 29 is accordingly quite similar to that of conventional gas tube thyratrons. Thus the average anode current of the device 29 is proportional to the number of pulses applied to the control gate electrode 28 of the device 29 over a given number of half cycles of the energizing voltage applied to the anode electrode, and by reason of this is proportional to the intensity of the radiation incident on the Geiger tube 10. It may be noted in this respect that when the rate at which pulses are applied to the control gate electrode 28 exceeds the nominal frequency of the exciting voltage supplied by the transformer 14, the average current of the anode electrode 31 does not increase substantially. This characteristic is useful in designing a go-no-go type of indicating and control system so that no recalibration is required after the initial installation, as by designing .the system such that approximately two to four pulses are applied to the control'gate electrode 28 from the Geiger tube 10 during each cycle of the voltage supplied by the transformer 14.

The resistor 39 and condenser 40 integrate the current of the anode electrode 31 of the device 29 over a number of cycles of the voltage of the transformer 14, and the relay 38 becomes sufliciently energized as to operate its relay contacts when the integrated current through the relay winding 37 reaches a predetermined value established by adjustment of the resistor 39. The relay contact operation may be used as desired for control of the stock feed or indications of stock level and distribution in the furnace, or as an indication that the radiation intensity lies above or below a preselected level (useful in indicating stock level with respect to a preselected level, for example). The meter 42 provides a measure of the average unidirectional current flowing in the circuit of the anode electrode 31 of the device 29, and thus is useful as a measure of the intensity of measured radiation or for monitoring and maintenance purposes.

Whereas the FIG. 1 indicating system has been shown and described as one having a high voltage unidirectional supply system for energizing the Geiger tube 10 and comprised by the diode rectifier 17, the condenser 18, and resistor 19, a modified form of the invention may dispense with this high voltage unidirectional supply and in lieu thereof energize the Geiger tube 10 directly from a high alternating voltage. This merely requires omission of the condenser 18 and resistors 16 and 19 from the FIG. 1 system and the short circuiting (i.e., removal) of the diode rectifier 17. This form of the invention, however, makes it advisable to use a form of Geiger tube having the construction shown in FIG. 2. The Geiger tube of FIG. 2 is generally of conventional construction and includes a cylindrical stainless steel housing 45, which comprises the cathode of the tube and includes an integrally formed anode terminal 46, and a coaxial small diameter tungsten anode 47. The latter is attached to the anode terminal 46 at the left end, and is insulated from the cathode 45 by a conventional insulator, and it is also insulated at the right end by an insulating disk 48 fixed in position within the right end of the housing 45. The disk 48 has a conical axial protuberance 49 over which a conductive Washer 50 is concentrically seated out of engagement with the housing 45 and sealed into place by a conventional.

potting compound suitably cured. A conductive insulated wire lead 51 is electrically connected'to the washer 50 and extends through an aperture 53 of a protective cap 54 of insulating material and which closes the right hand end of the housing 45. The wire lead 51 is electrically connected to the anode circuit of the Geiger tube, and the washer 50 and functions to establish a suitable electric field so as to minimize the potential difference between the filament and the insulator-exhaust top configuration. This avoids the generation of spurious signals during the A.C. operation of the Geiger tube.

It will be apparent from the foregoing description of the invention that a radiation indicating system embodying the invention avoids the use of all vacuum tubes other than the Geiger tube 10, and thus substantially improves the reliability of the system operation by reason of this fact. Reliability is also enhanced by the minimized number of system components used, and the use throughout the system of highly stable semiconductor devices renders the system less sensitive to the effects of humidity. The low impedance levels used throughout the system, including the cathode circuit of the Geiger tube causes the system to be relatively immune from the eifects of atmospheric and man-made electrical interference. The system exhibits such stable operating characteristics as to require substantially no recalibration after its initial installation calibration. System maintenance and trouble shooting are greatly simplified by the fact that the pulses generated by the Geiger tube 10 are directly translated to the indicating equipment rather than being converted at the Geiger tube location to a unidirectional potential which, in turn, is translated to the indicating equipment at a remote point. In fact, the pulses as thus translated to the remote indicating point by the system of the invention enable the pulses to be directly displayed on oscillographs or oscilloscopes or to be directly supplied to suitable scaling or counting equipments for direct radiation intensity calibration purposes.

While a specific from of invention has been described for purposes of illustration, it is contemplated that numerous changes may be made without departing from the spirit of the invention.

What is claimed is:

1. A nuclear radiation indicating system comprising first means exhibiting an inherent relatively high electrical source impedance for the generation of electrical pulses and responsive to nuclear radiation for generating timerandom electrical pulses having a time-rate value indicative of the intensity of said radiation, cyclic operating second means having an input circuit of relatively low electrical impedance and responsive during one-half of each cycle thereof to the first electrical pulse supplied to said input circuit during said each half cycle for initiating and thereafter continuing conduction of electrical current during substantially the remainder of each half cycle and for terminating conduction of said current during the succeeding half cycle, an output circuit electrically connecting said first means and said input circuit of said second means, impedance transforming means electric-ally connected in an output circuit of said first means for supplying said generated electrical pulses of said first means to said input circuit of said second means while transforming the high electrical impedance value of said first means to said low impedance value of said input circuit, and means included in the output circuit of said cyclic operating means and responsive to the time-averaged value of a characteristic of the current pulses of said cyclic operating means for indicating the relative intensity of said radiation.

2. A system according to claim -1, wherein the cyclic opera-ting means is energized by an alternating current source.

3. A system according to claim 1, wherein the cyclic operating means comprises a semi-conductor device.

4. A system according to claim 1, wherein the electrical pulse producing means comprises an ionization device in the form of a Geiger t-u be detector.

5. A system according to claim 4, wherein the Geiger tube is energized above the plateau region thereof and is responsive to nuclear radiation for generating by differentiation low-voltage short-duration electrical pulses.

6. A system according to claim 1, in which said pulses are transmitted to a remote point through said low impedance transmission line and the cyclic operating means is located at said remote point.

7. A system according to claim 1, wherein the differentiated electrical pulses are of the order of several microsecond pulse durations.

8. A system according to claim 1, wherein the cyclic operating means comprises a cyclic operating conductance-control means having a conductance-control electrode for receiving said pulses and being responsive during each of conductance hal-f cycles of said control means to the one of saidelectrical pulses first occurring during said each conductance halt cycle for initiating and thereafter continuing conduction of electrical current by said control means during substantially the remainder of said conductance half cycle, said conductance control means being non-conductive during the half cycle succeeding said each conductance half cycle.

9. A system according to claim 8, wherein the control means has during successive half cycles alternating conductable and non-conducta'b'le states, the conductancecontrol electrode being responsive to control potential of preselected polarity for initiating conduction during each said conductable state, and means being provided for supplying said pulses with said'preselected polarity to said conductance-control electrode to effect by the one of said pulses first occurring during said each conductable state of said control means initiation of conduction of electrical current thereby.

10. A system according to claim 8, wherein said impedance transforming means comprises an impedance matching network intercoupled by a low impedance electrical transmission line for differentiating and supplying said pulses with said preselected polarity to said conductance-control electrode.

11. A system according to claim 8, wherein the cyclic operating means comprises a unidirectionally conductive semi-conductive device, there being means for protecti-vely limiting the amplitude of pulses of said preselected polarity and of opposite polarity applied to said conductance-control electrode.

12. A system according to claim 9, wherein said impedance transforming means comprises a pair of impedance-matching pulse transformers intercoupled by a low impedance electrical transmission line for differentiating and supplying said pulses with said preselected 7 8 said low impedance transmission line to the primary wind- References Cited by the Applicant ing of the other of said transformers to develop in a se UNITED STATES PATENTS ondary winding of said second transformer differentiated 2,606,296 8/1952 pulses of short duration. Slmpson' 5 2,675,484 4/1954 Hepp. 2,708,721 5/1955 Zifier.

References Cited by the Examiner 2,824,237 2/1958 Witzel. I

UNITED STATES PATENTS 2,824,238 2/1958 Stellmacher; 2, 2/1958 Stellmacher 250-835 2,838,680 6/1958 Bender- 2,838,680 6/1958 Bender 250-335 10 2,909,663 10/1959 M l n FOREIGN PATENTS RALPH G. NILSON, Primary Examiner.

699,081 10/ 1953 Great Britain. JAMES W. LAWRENCE, Assistant Examiner. 

1. A NUCLEAR RADIATION INDICATING SYSTEM COMPRISING FIRST MEANS EXHIBITING AN INHERENT RELATIVELY HIGH ELECTRICAL SOURCE IMPEDANCE FOR THE GENERATION OF ELECTRICAL PULSES AND RESPONSIVE TO NUCLEAR RADIATION FOR GENERATING TIMERANDOM ELECTRICAL PULSES HAVING A TIME-RATE VALUE INDICATIVE OF THE INTENSITY OF SAID RADIATION, CYCLIC OPERATING SECOND MEANS HAVING AN INPUT CIRCUIT OF RELATIVELY LOW ELECTRICAL IMPEDANCE AND RESPONSIVE DURING ONE-HALF OF EACH CYCLE THEREOF TO THE FIRST ELECTRICAL PULSE SUPPLIED TO SAID INPUT CIRCUIT DURING SAID EACH HALF CYCLE FOR INITIATING AND THEREAFTER CONTINUING CONDUCTION OF ELECTRICAL CURRENT DURING SUBSTANTIALLY THE REMAINDER OF EACH HALF CYCLE AND FOR TERMINATING CONDUCTION OF SAID CURRENT DURING THE SUCCEEDING HALF CYCLE, AN OUTPUT CIRCUIT ELECTRICALLY CONNECTING SAID FIRST MEANS AND SAID INPUT CIRCUIT OF SAID SECOND MEANS, IMPEDANCE TRANSFORMING MEANS ELECTRICALLY CONNECTED IN AN OUTPUT CIRCUIT OF SAID FIRST MEANS FOR SUPPLYING SAID GENERATED ELECTRICAL PULSES OF SAID FIRST MEANS TO SAID INPUT CIRCUIT OF SAID SECOND MEANS WHILE TRANSFORMING THE HIGH ELECTRICAL IMPEDANCE VALUE OF SAID FIRST MEANS TO SAID LOW IMPEDANCE VALUE OF SAID INPUT CIRCUIT, AND MEANS INCLUDED IN THE OUTPUT CIRCUIT OF SAID CYCLIC OPERATING MEANS AND RESPONSIVE TO THE TIME-AVERAGED VALUE OF A CHARACTERISTIC OF THE CURRENT PULSES OF SAID CYCLIC OPERATING MEANS FOR INDICATING THE RELATIVE INTENSITY OF SAID RADIATION. 